Lyme disease presents a unique clinical system to study cellular and molecular mecahnisms responsible for chronic inflammatory diseases. The disease, caused by the spirochete Borrelia burgdorfen, is the most prevalent arthropod borne disease in the United States. It is a multisystemic illness that affects skin, muscles, joints, heart and nervous system. If left untreated, chronic manifestations are frequenctly observed and Lyme arthritis is the most common symptom in North America. My Iong term qoal is to identify the virulence factors of B. burgdorferi involved in attachment to host cells and in colonization of various tissues, and characterize their role in the pathogenesis, diagnosis and prevention of chronic Lyme disease. Glycosaminoglycans (GAGs), ubiquitously expressed on the surface of all nucleated cells, are recognized by various Lyme spirochetes and several bacterial molecules are involved in this adherence. Decorin binding lipoproteins DbpA and DbpB of B. burgdorferi show affinity for heparin and dermatan sulfate GAGs in addition to the proteoglycan decorin. My hypothesis is that DbpA and DbpB contribute to the colonization of various tissues by B. burgdorferi binding to GAGs and decorin present on the host cells and trigger an inflammatory response in skin and joints causing erythema migrans and Lyme arthritis. The major question to be addressed in this study are: (1) Do DbpA and DbpB contribute to the GAGsmediated attachment of B. burgdorferi to host cells and to the inflammatory response in the joints of susceptible mice? (2) Does deletion of dbpA and dbpB genes affect attachment of B. burgdorferi to the host cells? (3) Are DbpA and DbpB lipoproteins essential virulence factors of B. burgdorferi that trigger Lyme arthritis? Si,qniflcance: Lyme arthritis exhibits several symptoms similar to those of rheumatoid arthritis. However, unlike rheumatoid arthritis, the causative agent is known in Lyme disease and hence, it is feasible to analyze the molecular mechanisms involved in this form of destructive arthritis. In addition, B. burgdorfer/ infected mouse exhibits symptoms similar to those of human Lyme disease, and hence, murine model provides an ideal system to analyze the mechanisms of Lyme borreliosis. This study will characterize the role of two spirochete lipoprotein adhesins in Lyme arthritis in the murine model.